Inorganic adsorbent materials, such as molecular sieves, zeolites, etc., have long been used to remove constituents (especially water) from (gaseous and/or liquid) fluids. Zeolites such as zeolites A and X are widely used in desiccating and gas treatment applications.
In many instances, the adsorbent material is used in the form of a free flowing particulate (e.g. beads) which is allowed to contact the fluid to be treated. In other instances, the adsorbent may be embedded in a rigid monolithic structure such as a honeycomb. For many applications, these forms of the adsorbent cannot be used practically. For example, in the window spacer structures disclosed in U.S. Pat. Nos. 5,177,916 and 5,255,481, the adsorbent material is loaded into an organic matrix which is then adhered to the spacer. The disclosures of these window spacer patents are incorporated herein by reference.
In adsorbent/organic matrix composites, the adsorbent is typically incorporated into the organic matrix by mechanical mixing while the organic material is in a very soft or molten state. See for example, applicants co-pending U.S. patent application Ser. No. 08/304,312, filed Sep. 13, 1994, now abandoned, the disclosure of which is incorporated herein by reference. It is generally desirable to incorporate as much of the adsorbent material as possible per unit of organic matrix so as to enhance the adsorption performance of the adsorbent/organic matrix composite as well as to reduce the cost of the composite in situations where the organic matrix is more expensive than the adsorbent material.
Unfortunately, it has been found that many adsorbents (such as conventional potassium-containing 3A zeolites) are prone to degassing (i.e., gas evolution) during or after compounding with an organic matrix at elevated temperature. This degassing effect is especially pronounced at high adsorbent loadings and where the compounding temperature is high. Degassing leads to unsightly product appearance, unwanted expansion of the product after formulation, etc.
Unwanted gas adsorption/desorption (especially N.sub.2) may also occur where desiccating adsorbents are used in closed air-containing environments which are subject to fluctuations in temperature involving long holding times at or near the temperature limits of the fluctuation. For example, such situations may arise where conventional desiccant beads are used in a window which is exposed to a long term low temperature or high temperature condition.
While the degassing problem, in the context of compounded compositions, can be alleviated to some extent by heat treating the adsorbent immediately before compounding, such heat treating adds an extra step to the formulating process and requires the installation of additional equipment at the manufacturing site where the compounding is being performed. Thus, there is a need for adsorbent/organic matrix compositions which exhibit minimal or no degassing effect associated with the adsorbent while still functioning for the desired desiccation or adsorption application. There is also a need for desiccants which do not exhibit undesired gas adsorption/desorption behavior.